1. Field of the Invention
The present invention relates to a toner for use in electrophotography method, in image-forming methods that visualize an electrostatic image, and in toner jets.
2. Description of the Related Art
Higher speeds and greater reliability are being relentlessly pursued for image-forming apparatuses that use electrophotographic methods. In addition, the demands for better energy conservation on the part of the apparatus are also high, and in order to respond to these there is strong demand for an excellent low-temperature fixability on the part of the toner. The low-temperature fixability is generally related to the viscosity of the toner and requires an ability to rapidly melt when heated during fixing (the so-called sharp melt property). However, a toner that is satisfactory with regard to this low-temperature fixability is fragile with respect to external stresses such as stirring in the developing device and temperature increases in the unit, and problems then readily arise such as adhesion to machine components and a decline in durability because the external additives are embedded. In addition, in an image-forming apparatus whose speed has been increased, the printed recording paper is ejected on a short paper interval and accumulates in large amounts. As a result, the accumulated recording paper may stick to itself and become inseparable, or a magnetic toner that has undergone a single fixing may peel off and transfer to another sheet of paper. These are known as problems related to adhesion of ejected paper. This type of development readily appears in toners that have been endowed with low-temperature fixability in order to respond to high-speed printing, and having the low-temperature fixability co-exist with support for higher speeds is a very highly problematic technical hurdle.
Japanese Patent No. 3,015,244 and Japanese Patent Application Laid-open No. 2011-521294 propose the use of a polyester resin that has been at least partially modified with a compound that has a terminal hydroxyl group or carboxyl group and a long-chain alkyl group having a certain number of carbons. It is taught that this makes it possible to obtain a toner with an excellent charging stability, fixability, storage stability, and developing characteristics. However, in both cases, while a certain effect is seen on the low-temperature fixability, if too much focus is placed on improving the sharp melt property, recrystallization after heating during fixing is slow and the problems related to adhesion of ejected paper, supra, have a tendency to be significant.
Japanese Patent Application Laid-open No. 2011-81355 and Japanese Patent Application Laid-open No. 2010-107673 propose the use of an alkenyl group-containing amorphous polyester resin and a crystalline polyester that has an ester group concentration in a certain range. It is taught that this makes it possible to obtain an electrophotographic toner that, while providing an excellent low-temperature fixability, has an excellent charging stability at high temperatures and high humidities and an excellent storage stability. In these cases again, while a certain effect is seen on the low-temperature fixability, if too much focus is placed on improving the sharp melt property, recrystallization after heating during fixing is slow and the problems related to adhesion of ejected paper, supra, have a tendency to be significant. It is known that the recrystallization temperature of a crystalline material is generally lower than its melting point. Since, in order to improve upon the problems related to adhesion of ejected paper while delivering a satisfactory low-temperature fixability, a toner is required that melts at a low temperature and that recrystallizes at as high a temperature as possible, the technical hurdle here is very high.
In addition, in order to use the crystalline materials cited above, control of the state of existence within the polyester resin is critical. Materials that have very high plasticity, such as are used in the documents cited above, generally have a slow crystallization rate, and due to this they may recrystallize during storage, depending on the toner storage environment (temperature, humidity), and it may not be possible to realize the desired properties.
The proposal is made in Japanese Patent Application Laid-open No. 2003-98939 that the adhesion of ejected paper be stopped by cooling recording paper that has assumed a high temperature after fixing. However, improvements to the toner are required since the introduction of a cooling system into the machine is itself problematic for small desktop printers.
The proposal is made in Japanese Patent Application Laid-open No. 2003-302875 that adhesion of ejected paper be stopped by monitoring the temperature of the paper after ejection and modifying sequence in the unit (for example, opening up the paper interval) in correspondence to this temperature.
An improvement in adhesion of ejected paper is seen in this case also, but when one considers the productivity (number of prints made per unit time), this is a proposal that reduces the productivity and thus there is still room for improvement.
Thus, no proposal has yet been made wherein a better low-temperature fixability in an image-forming apparatus co-exists in good balance with improvements to the problems related to adhesion of ejected paper. This is because boosting the low-temperature fixability in association with increasing the speed and inhibiting adhesion of ejected paper post-fixing are antithetical effects, and having these co-exist in good balance is thus shown to be highly problematic.